In <oPydnQ9MUcW1vIPMnZ2dnUVZ_s6dnZ2d@giganews.com>, on 02/15/2013 at 05:50 AM, fom <fomJUNK@nyms.net> said:

>As this part of the construction had been>motivated by the axiom of regularity in>set theory, it is intuitively reasonable>to think of a letter as "a collection>of letters" although I suspect many will>find that objectionable.

Use of naive set theory leads to paradoxes. If you are using anymainstream set theory, e.g., ZFC, then no set is an element of itself.There are theories where you could get away with that, e.g., NF, but Isuspect that you would find them awkward. More to the point, having aletter be a collection of letters would violate the very axiom ofregularity that you cite as your motivation.

Things like that are more reasonable in Mereology, about which I don'tknow much, but if you're addressing issues related to set theory thatdoesn't help.